CloudFlare CDN allows Brotli OR GZIP or none.
So, Pingdom validates only GZIP or none.
Maybe I am wrong but even I verify other testing websites it will be GZIP enabled, Brotli enabled but Pingdom will report just GZIP verification.
As CloudFlare allows compressed method (Brotli), it means Pingdom pushes GZIP validation as 45/100 as false result.
Gzip was originally intended to compress files and has been adapted to compressing streams so it could work on the web. Brotli on the other hand, was designed from the beginning to compress streams. This makes it a better choice for web servers to compress content before streaming it to a browser.